Continuous aggregates are often used to downsample historical data. If the data is only used for analytical queries and never modified, you can compress the aggregate to save on storage.
Compression on continuous aggregates works similarly to compression on hypertables. Compressed chunks can be queried, but they can't be updated or deleted. For continuous aggregates, that means compressed chunks can't be refreshed.
If you receive historical data and need to refresh a compressed chunk, see the troubleshooting guide.
You can't refresh the compressed regions of a continuous aggregate. To avoid conflicts between compression and refresh, make sure you set
compress_after to a larger interval than the
start_offset of your refresh policy.
You can enable and disable compression on continuous aggregates by setting the
compress parameter when you alter the view.
For an existing continuous aggregate, at the
psqlprompt, enable compression:ALTER MATERIALIZED VIEW cagg_name set (timescaledb.compress = true);
Disable compression:ALTER MATERIALIZED VIEW cagg_name set (timescaledb.compress = false);
Disabling compression on a continuous aggregate fails if there are compressed chunks associated with the continuous aggregate. In this case, you need to decompress the chunks, and then drop any compression policy on the continuous aggregate, before you disable compression. For more detailed information, see the decompress chunks section:
SELECT decompress_chunk(c, true) FROM show_chunks('cagg_name') c;
Before setting up a compression policy on a continuous aggregate, you should set up a refresh policy. The compression policy interval should be set so that actively refreshed regions are not compressed. This is to prevent refresh policies from failing. For example, consider a refresh policy like this:
SELECT add_continuous_aggregate_policy('cagg_name',start_offset => INTERVAL '30 days',end_offset => INTERVAL '1 day',schedule_interval => INTERVAL '1 hour');
With this kind of refresh policy, the compression policy needs the
compress_after parameter greater than the
start_offset parameter of the
continuous aggregate policy:
SELECT add_compression_policy('cagg_name', compress_after=>'45 days'::interval);
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